Nitrided mixed oxide catalyst system and a process for the production of ethylenically unsaturated carboxylic acids or esters

ABSTRACT

The invention relates to a method of producing an ethylenically unsaturated carboxylic acid or ester, preferably an α, β ethylenically unsaturated carboxylic acid or ester. The method includes contacting formaldehyde or a suitable source thereof with a carboxylic acid or ester in the presence of a catalyst and optionally in the presence of an alcohol. The catalyst comprises a nitrided metal oxide having at least two types of metal cations, M 1  and M 2 , wherein M 1  is selected from the metals of group 2, 3, 4, 13 (called also IIIA) or 14 (called also IVA) of the periodic table and M2 is selected from the metals of groups 5 or 15 (called also VA) of the periodic table. The invention extends to a catalyst system.

RELATED APPLICATIONS

This U.S. Non-Provisional application is a Divisional Application of andclaims priority from U.S. Non-Provisional patent application Ser. No.13/805,413 filed on Mar. 1, 2013, which claims priority fromPCT/GB2011/051195 filed on Jun. 24, 2011, which claims priority from GBApplication 1011092.2 filed on Jul. 1, 2010. Each of the above mentionedApplications are herein incorporated by reference in its entirety.

TECHNICAL FIELD AND BACKGROUND OF THE INVENTION

The present invention relates to nitrided mixed oxide catalysts and aprocess for the production of ethylenically unsaturated carboxylic acidsor esters, particularly α, β unsaturated carboxylic acids or esters,more particularly (alk)acrylic acids or alkyl (alk)acrylates such as(meth)acrylic acid or alkyl (meth)acrylates by the condensation ofcarboxylic acids or esters with a methylene or ethylene source, such asformaldehyde or a suitable source thereof in the presence of nitridedmixed oxide catalysts. In particular, but not exclusively, the inventionrelates to a process for the production of (meth) acrylic acid or alkylesters thereof, for example, methyl methacrylate, by the condensation ofpropionic acid or alkyl esters thereof with formaldehyde or a sourcethereof in the presence of such nitrided mixed oxide catalysts.

SUMMARY OF THE INVENTION

Such acids or esters can be considered as being produced formulaicallyby reacting an alkanoic acid (or ester) of the formula R³—CH₂—COOR⁴,where R³ and R⁴ are each, independently, a suitable substituent known inthe art of acrylic compounds such as hydrogen or an alkyl group,especially a lower alkyl group containing, for example, 1-4 carbonatoms, with a suitable methylene source, for example, a source offormaldehyde. Thus, for instance, methacrylic acid or alkyl estersthereof, especially methyl methacrylate, may be made by the catalyticreaction of propionic acid, or the corresponding alkyl ester, e.g.methyl propionate, with formaldehyde as a methylene source in accordancewith the reaction sequence 1.

R³—CH₂—COOR⁴+HCHO------>R³—CH(CH₂OH)—COOR⁴

and

R³—CH(CH₂OH)—COOR⁴------>R³—C(:CH₂)—COOR⁴+H₂O

Sequence 1

An example of reaction sequence 1 is reaction sequence 2

CH₃—CH₂—COOR⁴+HCHO------->CH₃—CH(CH₂OH)—COOR⁴

CH₃—CH(CH₂OH)—COOR⁴------>CH₃—C(:CH₂)—COOR⁴+H₂O

Sequence 2

The above reaction Sequence 1 or 2 is typically effected at an elevatedtemperature, usually in the range 250-400° C., using an acid/basecatalyst. Where the desired product is an ester, the reaction ispreferably effected in the presence of the relevant alcohol in order tominimise the formation of the corresponding acid through hydrolysis ofthe ester. Also for convenience it is often desirable to introduce theformaldehyde in the form of formalin. Hence, for the production ofmethyl methacrylate, the reaction mixture fed to the catalyst willgenerally consist of methyl propionate, methanol, formaldehyde andwater.

Conventionally, methyl methacrylate has been produced industrially viathe so-called acetone-cyanohydrin route. The process is capitalintensive and produces methyl methacrylate at a relatively high cost.

U.S. Pat. No. 4,560,790 describes the production of α, β unsaturatedcarboxylic acids and esters by the condensation of methylal with acarboxylic acid or ester using a catalyst of general formula M¹/M²/P/Owherein M¹ is a group IIIb metal, preferably aluminium, and M² is agroup IVb metal, preferably silicon.

Sumitomo have disclosed metal oxynitride catalysts for the preparationof α,β-unsaturated products using formaldehyde, JP 2005-213182A,nitriding single metal oxides such as Ta₂O₅ by thermal treatment withammonia. The resultant oxynitrides catalysed the gas-phase condensationof formaldehyde (trioxane source) with propionic acid to methacrylicacid. Sumitomo also disclose the possibility of putting these singlemetal oxides on a support such as silica or alumina.

EP 1 243 574 discloses the use of Aluminium phosphates,silicoaluminophosphates and mesoporous amorphous alumina-silica andtheir nitrided or oxynitrided equivalents to catalyse the mixed aldolcondensation of an n-alkylaldehyde and benzaldehyde toα-n-amylcinnamaldehyde. No noticeable improvement for the nitridedcatalysts was found or taught. There is no disclosure of the use of asupport. In fact, an increase in the yield of side products was notedfor the nitrided catalysts.

As mentioned above, a known production method for MMA is the catalyticconversion of methyl propionate (MEP) to MMA using formaldehyde. Asuitable catalyst for this is a caesium catalyst on a support, forinstance, silica.

The inventors have analysed for comparison the effect of nitriding thesilica support. Unmodified silica is effectively inert in thecondensation reaction between formaldehyde and propionic acid to produceMMA. Nitridation of the silica introduced a very low activity, givingsmall yields of MMA and methacrolein. The catalytic performance ofnitrided silica was very similar to that of silicon nitride (Si₃N₄),which has a hydrated surface analogous to that of silica. Therefore,compared to Cs impregnated silica, nitrided silica is not suitable foruse in the condensation reaction between formaldehyde and a carboxylicacid or ester to produce MMA.

However, it has now been found that a particular combination of metaloxidation states in a mixed metal oxide that has been nitrided canprovide a surprisingly high selectivity for the ethylenicallyunsaturated carboxylic acids or ester product in the reaction of amethylene or ethylene source such as formaldehyde, or a suitable sourcethereof with a carboxylic acid or ester to produce ethylenicallyunsaturated carboxylic acids or esters, particularly α, β ethylenicallyunsaturated carboxylic acids or esters.

According to a first aspect of the present invention there is provided amethod of producing an ethylenically unsaturated carboxylic acid orester, preferably an α, β ethylenically unsaturated carboxylic acid orester, comprising the steps of contacting formaldehyde or a suitablesource thereof with a carboxylic acid or ester in the presence of acatalyst and optionally in the presence of an alcohol, wherein thecatalyst comprises a nitrided metal oxide having at least two types ofmetal cations, M¹ and M², wherein M¹ is selected from the metals ofgroup 2, 3, 4, 13 (called also IIIA) or 14 (called also IVA) of theperiodic table and M² is selected from the metals of groups 5 or 15(called also VA) of the periodic table.

It will be appreciated by the skilled person that the invention isdistinct from the existence of an incidental molecular monolayer of anitrided single metal oxide catalyst formed on a support of anothermetal oxide. However, for the avoidance of doubt, typically, thecatalyst cations, M¹ and M², and oxide and nitride anions are uniformlydistributed throughout the nitrided metal oxide catalyst which catalystextends to multiple molecular layers, more typically, at least 2 nm,most typically, at least 5 nm, especially, at least 10 nm averagethickness. This would not be the case with a single nitrided metal oxidelayer on a support where the metal of the support only interacts at thelevel of the catalyst molecular monolayer on the support (typically,about 1 nm thick) and not throughout the catalyst. Furthermore, in theinvention, the metal cations, M¹ and M² and the oxide and nitride of thecatalyst are exclusively from the catalyst and not from a support forthe catalyst. Thus, in general, the catalyst of the invention is not amolecular monolayer on a support for the catalyst but a multi-layeredcatalyst having the properties defined in the invention throughout itssubstance.

Thus, in general, the cations or anions forming the nitrided metal oxidecatalyst are not simultaneously metal cations or anions of a catalyticsupport unless, independent of the support, the catalyst is inaccordance with the invention throughout its substance.

Typically, the nitrided metal oxide of the present invention exists andis used independently of any catalytic support. However, when used on asupport, the nitrided mixed metal oxide provides a nitrided mixed metaloxide catalytic surface having M¹ type and M² type cations and oxygenand nitrogen anions independently of any metal cations and oxygen ornitrogen anions forming or contributed by the support.

According to a second aspect of the present invention there is provideda catalyst system for the reaction of formaldehyde or a suitable sourcethereof with a carboxylic acid or ester, optionally in the presence ofan alcohol, to produce an ethylenically unsaturated carboxylic acid orester, preferably α, β ethylenically unsaturated carboxylic acids oresters, wherein the catalyst comprises a nitrided metal oxide having atleast two types of metal cations, M¹ and M², wherein M¹ is selected fromat least two metals of group 2, 3, 4, 13 (called also IIIA), 14 (calledalso IVA) of the periodic table and M² is selected from at least onemetal of group 5 or at least one metal of group 15 (called also VA) inthe 4^(th) to 6^(th) periods of the periodic table.

In addition to the high selectivity achieved by the catalysts of thepresent invention, use of the catalyst of the present invention has beenfound to produce remarkably low levels of unwanted side products in thereaction of formaldehyde or a suitable source thereof with a carboxylicacid or ester to produce an ethylenically unsaturated carboxylic acid orester. In particular, remarkably low levels of methyl isobutyrate (MIB),toluene and diethyl ketone compared to conventional catalysts such asaluminium phosphate. In addition, the catalysts provide excellentactivity.

The present invention thus advantageously provides a successful methodof improving the selectivity of strongly acidic catalysts. The highselectivity (up to 95%) obtained with the nitrided catalysts indicatesthat acid-type catalysis can provide viable ethylenically unsaturatedcarboxylic acid or ester selectivity.

Preferably, the nitrided mixed oxide is prepared by nitriding the mixedoxide. Typically, short nitridation treatments of between 3 and 15 hoursare found to be effective in the nitridation of the catalytic surface.However, shorter or longer nitridations can be carried out depending onthe nitridation conditions and substrates.

Preferably, the nitrided mixed oxide consists of two to four metalcations, and oxygen and nitrogen anions.

A preferred formula for the mixed oxide is therefore M¹ _(x)M² _(y)O_(n)wherein M¹ is one or more 2+, 3+ or 4+ cations and M² is a 5+ cationwherein x is the number of M¹ atoms, y is the number of M² atoms and nis the number of oxygen atoms. Thus the nitrided metal oxide may begiven by formula M¹ _(x)M² _(y)O_(n)N_(z) wherein z is the averagenumber of nitrogen atoms and wherein x, y, n and z may each be a decimalnumber or positive integer. Generally, x, y, n and z may independentlybe between 0.1 and 20, more preferably, between 0.1 and 10, mostpreferably, between 0.1 and 5. In a particularly preferred formula x andy are both 1 and n and z are numbers which provide the anionic balanceto the cationic charge of M¹ and M².

Typically, the M¹ type of metal may be selected from one or more metalsin the list consisting of:—Be, Mg, Ca, Sr, Ba, Ra, B, Al, Ga, In, Tl,Sc, Y, La, Ac, Si, Ge, Sn, Pb, Ti, Zr, Hf, Rf more preferably, Al, Ga orLa, most preferably, Al.

Typically, the M² type of metal in the process of the present inventionmay be selected from one or more metals in the list consistingof:—P(5+), Nb(5+), As (5+) Sb(5+), or Ta(5+), more preferably, P(5+),Nb(5+) or Sb(5+), most preferably, P(5+). Typically, the M² type ofmetal in the catalyst invention of the second aspect of the presentinvention may be selected from one or more metals in the list consistingof: —Nb(5+), As (5+) Sb(5+) or Ta(5+), more preferably, Nb(5+) orSb(5+), most preferably, Nb(5+).

Advantageously, using a mixture of metals of the type M¹ gives moreflexibility in modifying the acid-base balance of the catalyst. Inparticular, a further M¹ metal can be introduced to provide an increaseor decrease in acidity as appropriate. Preferred M¹ modifier metals forthis purpose are barium and lanthanum.

Preferably, M¹ is/are cation(s) in the 3+ oxidation state. Preferably,M² is a cation in the +5 oxidation state.

Assuming nitrogen is not a metal, said metal cations of the type M¹ andM², whether one or more of each type is present, may form from 90 to 100mol % of the total metal present in the mixed metal oxide, moreespecially, 95-100 mol %, most especially, 97-100 mol %, particularly,substantially 100 mol %. If another metal of the type M³ set out belowis present and/or another metal type, the metals of the type M¹ and M²may form up to 99.99 or 99.89 or 99.90 mol % of the total metal present,more typically, up to 99.90 or 99.80 mol % of the total metal present inthe metal oxide with the same lower limits as already set out above.

Preferably, oxygen and nitrogen may form from 50 to 100 mol % of thetotal non-metal present in the metal oxide of the invention, morepreferably, 70-100 mol % of the total non-metal present in the metaloxide, most preferably, 80-100 mol % of the total non-metal present,especially, 90-100 mol % of the total non-metal present in the metaloxide, more especially, 99%-100 mol %, most especially, substantially100 mol %.

For the avoidance of doubt, non-metals herein does not include the“metalloid” elements boron, silicon, phosphorus, germanium, arsenic,antimony, tellurium and polonium but includes all elements having higheratomic numbers than the named element(s) in their respective period ofthe periodic table.

Preferably, the nitrided metal oxide forms 50-100 wt % of the catalyst,more preferably, 80-100 wt %, most preferably, 90-100 wt %, especially,95-100 wt %, more especially, 97-100 wt %, most especially, 99-100 wt %of the catalyst. The balance of the catalyst is made up of impurities,binders or inert materials. Generally, the nitrided metal oxide formsabout 100% of the catalyst.

However, when a binder is used in the present invention it may form upto 50 wt % of the catalyst. Alternatively, the binder may be used inconjunction with a catalyst support to bind the catalyst to the support.In the latter case, the binder does not form part of the catalyst assuch.

Suitable binders for the catalyst of the present invention will be knownto those skilled in the art. Non-limiting examples of suitable bindersinclude silica (including colloidal silica), silica-alumina, such asconventional silica-alumina, silica-coated alumina and alumina-coatedsilica, and alumina, such as (pseudo)boehmite, gibbsite, titania,titania-coated alumina, zirconia, cationic clays or anionic clays suchas saponite, bentonite, kaolin, sepiolite or hydrotalcite or mixturesthereof. Preferred binders are silica, alumina and zirconia or mixturesthereof

The nitrided metal oxide particles can be embedded in the binder or viceversa. Generally, when used as part of the catalyst, the binderfunctions as an adhesive to hold the particles together. Preferably, theparticles are homogeneously distributed within the binder or vice versa.The presence of the binder generally leads to an increase in mechanicalstrength of the final catalyst.

The typical average surface area of the metal oxide catalyst is in therange 2-1000 m²g⁻¹, more preferably, 5-400 m²g⁻¹, most preferably,10-300 m²g⁻¹ as measured by the B.E.T. multipoint method using aMicromeritics TriStar 3000 Surface Area and porosity Analyser. Thereference material used for checking the instrument performance is acarbon black powder supplied by Micromeritics with a surface area of30.6 m²/g (+/−0.75 m²/g), part number 004-16833-00.

The typical average particle size of the catalyst particles is in therange 2 nm-10000 nm (10μ), more preferably, 5 nm-4000 nm (4μ), mostpreferably, 10 nm-3000 nm (3μ) as measured by a Malvern Zetasizer Nano Susing dynamic light scattering and using NIST standards.

If the material is porous, it is preferably mesoporous with an averagepore size of between 2 and 50 nm. Pore size can be determined by mercuryintrusion porosimetry using NIST standards.

The average pore volume of the catalyst particles may be less than 0.01cm³/g but is generally in the range 0.01-2 cm³/g as measured by nitrogenadsorption. However, microporous catalysts are not the most preferredbecause they may inhibit movement of reagents through the catalyst and amore preferred average pore volume is between 0.3-1.2 cm³/g as measuredby BET multipoint method using nitrogen adsorption according to ISO15901-2:2006. The Micromeritics TriStar Surface Area and PorosityAnalyser is used to determine pore volume as in the case of surface areameasurements and the same standards are employed.

In the case of a non supported catalyst, the nitrided metal oxide may beused directly in the form of a catalyst particles either free flowing ortogether with a suitable binder to create a solid of the desired shapeand/or size. The particles may be of any suitable size and thereforealso in the form of powder, granules or beads either with or withoutbinder. Typically, the catalyst is used in the form of a fixed bed andfor this purpose may be used alone or on a support and in the lattercase may include a suitable catalytic binder to bind it to the support.

However, it is also possible for the catalyst to be used on a support.In this case, the nitrided metal oxide catalyst may form a suitablesurface coating on a suitable support for a catalyst.

For the purposes of the present invention, the support does not formpart of the catalyst.

Preferred combinations of nitrided metal oxides for use in the presentinvention may be selected from the list consisting of: —AlPON; ZrPON;SnPON; ZrNbON; GaSbON; and GaAlPON. These oxides are either unsupportedor supported on a suitable support, for example, alumina, silica,silicon nitride, colloidal silica, titania or aluminium phosphate.

It will be understood by the skilled person that a catalyst of theinvention may be added to a support by any suitable means. The catalystmay be fixed, preferably by calcination, onto a suitable support afterdeposition of the compound onto the support using a suitable salt in asuitable solvent and subsequent drying of the surface coated support.Alternatively, the catalyst or suitable catalyst salt precursors may beco-precipitated with the support or suitable support precursors such asa silica sol from a suitable solvent. Preferably, an oxide support isused, more preferably, an oxide support as mentioned herein.

It is also possible to use the catalyst of the present invention in amixture or admixture with another catalyst according to the presentinvention or otherwise with or without a suitable binder. The totallevel of nitrided mixed oxides, cations and anions and binder may be thesame as set out herein.

However, a distinction should be drawn between a metal compoundaccording to the invention and a monolayer of a metal compound on ametal oxide support or a nitrogen containing support where one or morecomponents, metal M¹/M² and/or oxygen and/or nitrogen is provided by thesurface compound and the other components, metal M²/M¹ and/or nitrogenand/or oxygen is provided by the support. Such a monolayer arrangementis not a catalyst according to the present invention but rather adifferent catalyst which is supported. In this arrangement, the elementsM¹, M², N and O do not form a catalyst according to the inventionthroughout the catalyst material. The surface coating will consist ofmultiple layers and the layers other than the monolayer will not conformto the invention.

As mentioned above, although at least one metal of the type M¹ and onemetal of the type M² are present in the catalyst, further metals ormetal cations of the type M³ may also be present in the mixed metaloxide. Typically, when present, the at least one metal M³ whether in theform of a cation or otherwise may form between 0.01 and 10 mol % of thetotal metal present, more preferably, 0.01-5 mol % of the total metalpresent, most preferably, 0.1-3 mol % of the total metal present in themetal oxide. Suitable M³ metals include metals from group I of theperiodic table, more preferably, lithium, sodium, potassium, rubidiumand/or caesium.

Preferably, no other metal types are present in the metal oxide catalystcompound of the present invention above a total other metal level of 0.1mol % other than the types M¹, M² and optionally M³ as all definedherein, more typically, no other metal types are present in the metaloxide catalyst compound of the present invention above a trace levelthan the types M¹, M² and optionally M³ as all defined herein.

Typically, it is possible to include two or more metals of the type M¹and/or M² within the scope of the present invention, more typically, upto three metals of each type M¹ and/or M², most typically, up to twometals of each type M¹ and/or M², especially, up to two metals of onetype and only one metal of the other type, more especially, only onemetal of each type M¹ and M²: all the above being possible with orwithout any one or more metals of the type M³.

Preferably, including the at least one M¹ and M² metal, the metal oxidecompound may have up to four or more preferably up to three metalcations in total, most preferably, however, there are only two metalcations in the metal oxide. Therefore, it is especially preferred thatthe metal oxide compound consists of one or two each, more especially,one each of the metal cations M¹ and M² together with oxygen anions.

A further preferred formula for the nitrided metal oxide is therefore M¹_(n)M² _(m)M³ _(q)O_(p)N_(s) wherein M¹ is a cation, preferably, a 3+cation and M² is a cation, preferably, a 5+ cation, n, m, p and s may bea positive integer or decimal number and q may be a positive integer ordecimal number or zero. Generally, n and m may independently be between0.1 and 20, more preferably, between 0.1 and 10, most preferably,between 0.1 and 5 whereas s is the required molecular level ofnitridation and p is a number which provides the balance to theremaining positive charge provided by n and m which is not balanced bys. Generally, q may be between 0 and 20, more preferably, 0.1 and 10,most preferably, 0.1 and 5. In a particularly preferred formula n and mare both 1. For the avoidance of doubt, the values on n, m and q definedabove are also the total relative number for M¹, M², M³ _(type) metalsif more than one cation of each type is present.

Generally, the nitrided metal oxide of the present invention is aneutral molecule and therefore the negatively charged oxygen andnitrogen anions and optionally, any other non-metals balance thepositively charged metals present.

Preferably, the mole ratio of oxygen to nitrogen in the nitrided mixedmetal oxide is in the range 1:1 to 400:1, more preferably, 2:1 to 100:1,most preferably, 3:1 to 40:1.

Preferably, the level of nitrogen in the nitrided mixed metal oxide isin the range 0.1 to 50 wt %, more preferably, 0.5 to 20 wt %, mostpreferably, 1 to 15 wt %. However, it will be appreciated that the wt %of nitrogen and oxygen in the nitrided mixed metal oxide will depend onthe molecular weight of the metals selected.

Preferably, the nitrided mixed oxide consists of the metal cations M¹and M² and oxygen and nitrogen anions. For the avoidance of doubt,generally, only a single metal of each type is present. However, it isalso possible to include two or more metals of the type M¹ and/or M²within the context of the present invention.

As mentioned herein, the term nitrided metal oxide should be understoodin the general chemical sense as an ionic or covalent compound havingthe general formula (M′)_(n)(M²)_(m)(M³)_(q)O_(p)N_(s) wherein n and mmust be greater than 0 and can take a decimal value and q isindependently greater than or equal to 0 and can also take a decimalvalue. Generally, a mainly ionic compound is formed by the nitridedmetal oxides of the present invention. The metal oxide compound itselfof the present invention should not be understood in anynon-conventional sense as relating to an admixture of metals and/ornitrides, oxides which do not form new nitrided oxide compounds asdefined herein.

The mole ratio of M¹ to M² type is generally in the range 10:1 to 1:10,more preferably, 5:1 to 1:5, most preferably, 3:1 to 1:3, especially,2:1 to 1:2, more especially approximately 1:1. It will be appreciatedthat oxygen and nitrogen will generally be present at a level to balancethe total cationic charge.

The mixed metal oxide compound may be supported on a suitable supportsuch as silica, silicon nitride, colloidal silica, alumina, titania oraluminium phosphate. The support may or may not be an alkali metal dopedsupport. If the support is alkali metal doped, the alkali metal dopingagent may be selected from one or more of caesium, potassium, sodium, orlithium, preferably, caesium or potassium, more preferably, caesium.Alternatively, the mixed oxide may itself be doped with any one or moreof the above mentioned doping metals representing M³, particularly thoseof group I above.

Preferably, when a separate support for the catalyst of the first orsecond aspect is used, the weight ratio of catalyst:support is in therange 10:1 to 1:50, more preferably, 1:1 to 1:20, most preferably, 2:3to 1:10.

Advantageously, unsaturated ester selectivity is increased by dopingcations having a low charge to radius ratio thus caesium was found to bemore selective than lithium. Preferably, therefore, if used, the dopingmetal cation is caesium, rubidium and/or potassium, more preferably,rubidium and/or caesium, most preferably caesium.

Preferably, the carboxylic acid or ester reactant of the presentinvention is of formula R³—CH₂—COOR⁴ wherein R⁴ is either hydrogen or analkyl group and R³ is either hydrogen, an alkyl or aryl group.

According to a further aspect of the present invention there is provideda production process for the manufacture of ethylenically unsaturatedcarboxylic acids or esters thereof, preferably, an α, β ethylenicallyunsaturated carboxylic acid or ester, comprising the steps of contactingan alkanoic acid or ester of the formula R³—CH₂—COOR⁴ with formaldehydeor a suitable source thereof, optionally in the presence of an alcohol,wherein R³ and R⁴ are each independently hydrogen or an alkyl group andR³ may also be an aryl group, in the presence of a catalyst effective tocatalyse the reaction, wherein the catalyst is in accordance with thefirst aspect of the present invention.

A suitable source of formaldehyde may be a compound of formula I

wherein R⁵ and R⁶ are independently selected from C₁-C₁₂ hydrocarbons orH, X is O, n is an integer from 1 to 100, and m is 1.

Preferably, R⁵ and R⁶ are independently selected from C₁-C₁₂ alkyl,alkenyl or aryl as defined herein, or H, more preferably, C₁-C₁₀ alkyl,or H, most preferably, C₁-C₆ alkyl or H, especially, methyl or H.Preferably, n is an integer from 1 to 10, more preferably 1 to 5,especially, 1-3.

However, other sources of formaldehyde may be used including trioxane.

Therefore, a suitable source of formaldehyde includes any equilibriumcomposition which may provide a source of formaldehyde. Examples of suchinclude but are not restricted to methylal (1,1 dimethoxymethane),trioxane, polyoxymethylenes R¹—O—(CH₂—O)_(i)—R² wherein R¹ and/or R² arealkyl groups or hydrogen, i=1 to 100, paraformaldehyde, formalin(formaldehyde, methanol, water) and other equilibrium compositions suchas a mixture of formaldehyde, methanol and methyl propionate.

Typically, the polyoxymethylenes are higher formals or hemiformals offormaldehyde and methanol CH₃—O—(CH₂—O)_(i)—CH₃ (“formal-i”) orCH₃—O—(CH₂—O)_(i)—H (“hemiformal-i”), wherein i=1 to 100, preferably,1-5, especially 1-3, or other polyoxymethylenes with at least one nonmethyl terminal group. Therefore, the source of formaldehyde may also bea polyoxymethylene of formula R³¹—O—(CH2-O—)_(i)R³², where R³¹ and R³²may be the same or different groups and at least one is selected from aC₂-C₁₀ alkyl group, for instance R³¹=isobutyl and R³²=methyl.

Preferably, the suitable source of formaldehyde is selected frommethylal, higher hemiformals of formaldehyde and methanol,CH₃—O—(CH₂—O)_(i)—H where i=2, formalin or a mixture comprisingformaldehyde, methanol and methyl propionate.

Preferably, by the term formalin is meant a mixture offormaldehyde:methanol:water in the ratio 25 to 65%: 0.01 to 25%: 25 to70% by weight. More preferably, by the term formalin is meant a mixtureof formaldehyde:methanol:water in the ratio 30 to 60%: 0.03 to 20%: 35to 60% by weight. Most preferably, by the term formalin is meant amixture of formaldehyde:methanol:water in the ratio 35 to 55%: 0.05 to18%: 42 to 53% by weight.

Preferably, the mixture comprising formaldehyde, methanol and methylpropionate contains less than 5% water by weight. More preferably, themixture comprising formaldehyde, methanol and methyl propionate containsless than 1% water by weight. Most preferably, the mixture comprisingformaldehyde, methanol and methyl propionate contains 0.1 to 0.5% waterby weight.

Preferably, the ethylenically unsaturated acid or ester produced by theprocess of the invention is selected from methacrylic acid, acrylicacid, methyl methacrylate, ethyl acrylate or butyl acrylate; morepreferably, it is an ethylenically unsaturated ester, most preferably,methyl methacrylate.

The process of the invention is particularly suitable for the productionof acrylic, alkacrylic, 2-butenoic, cyclohexenoic, maleic, itaconic andfumaric acids and their alkyl esters. Suitable, alkacrylic acids andtheir esters are (C₀₋₈alk)acrylic acid or alkyl (C₀₋₈alk)acrylates,typically from the reaction of the corresponding alkanoic acid or esterthereof with a methylene source such as formaldehyde in the presence ofthe catalyst, preferably the production of methacrylic acid orespecially methyl methacrylate(MMA) from propanoic acid or methylpropionate respectively.

The reaction of the present invention may be a batch or continuousreaction.

The term “alkyl” when used herein, means, unless otherwise specified, C₁to C₁₂ alkyl and includes methyl, ethyl, ethenyl, propyl, propenylbutyl, butenyl, pentyl, pentenyl, hexyl, hexenyl and heptyl groups,preferably, methyl, ethyl, propyl, butyl, pentyl and hexyl. Unlessotherwise specified, alkyl groups may, when there is a sufficient numberof carbon atoms, be linear or branched, be cyclic, acyclic or partcyclic/acyclic, be unsubstituted, substituted or terminated by one ormore substituents selected from halo, cyano, nitro, —OR¹⁹, —OC(O)R²⁰,—C(O)R²¹, —C(O)OR²², —NR²³R²⁴, —C(O)NR²⁵R²⁶, —SR²⁹, —C(O)SR³⁰,—C(S)NR²⁷R²⁸, unsubstituted or substituted aryl, or unsubstituted orsubstituted Het, wherein R¹⁹ to R³⁰ here and generally herein eachindependently represent hydrogen, halo, unsubstituted or substitutedaryl or unsubstituted or substituted alkyl, or, in the case of R²¹,halo, nitro, cyano and amino and/or be interrupted by one or more(preferably less than 4) oxygen, sulphur, silicon atoms, or by silano ordialkylsilcon groups, or mixtures thereof. Preferably, the alkyl groupsare unsubstituted, preferably, linear and preferably, saturated.

The term “alkenyl” should be understood as “alkyl” above except at leastone carbon carbon bond therein is unsaturated and accordingly the termrelates to C₂ to C₁₂ alkenyl groups.

The term “alk” or the like should, in the absence of information to thecontrary, be taken to be in accordance with the above definition of“alkyl” except “C₀ alk” means non-substituted with an alkyl.

The term “aryl” when used herein includes five-to-ten-membered,preferably five to eight membered, carbocyclic aromatic or pseudoaromatic groups, such as phenyl, cyclopentadienyl and indenyl anions andnaphthyl, which groups may be unsubstituted or substituted with one ormore substituents selected from unsubstituted or substituted aryl, alkyl(which group may itself be unsubstituted or substituted or terminated asdefined herein), Het (which group may itself be unsubstituted orsubstituted or terminated as defined herein), halo, cyano, nitro, OR¹⁹,OC(O)R²⁰, C(O)R²¹, C(O)OR²², NR²³R²⁴, C(O)NR²⁵R²⁶, SR²⁹, C(O)SR³⁰ orC(S)NR²⁷R²⁸ wherein R¹⁹ to R³⁰ each independently represent hydrogen,unsubstituted or substituted aryl or alkyl (which alkyl group may itselfbe unsubstituted or substituted or terminated as defined herein), or, inthe case of R²¹, halo, nitro, cyano or amino.

The term “halo” when used herein means a chloro, bromo, iodo or fluorogroup, preferably, chloro or fluoro.

Without prejudice to the scope of protection and without being bound bytheory, upon making this surprising discovery, the inventors testedwhether there may be a diene impurity that was causing the colouration.However, reaction with the dienophile does not seem to affect the dieneimpurities identified, indicating that the impurity may not be a diene.

The term “Het”, when used herein, includes four- to twelve-membered,preferably four- to ten-membered ring systems, which rings contain oneor more heteroatoms selected from nitrogen, oxygen, sulfur and mixturesthereof, and which rings contain no, one or more double bonds or may benon-aromatic, partly aromatic or wholly aromatic in character. The ringsystems may be monocyclic, bicyclic or fused. Each “Het” groupidentified herein may be unsubstituted or substituted by one or moresubstituents selected from halo, cyano, nitro, oxo, alkyl (which alkylgroup may itself be unsubstituted or substituted or terminated asdefined herein) —OR¹⁹, —OC(O)R²⁰, —C(O)R²¹, —C(O)OR²², —N(R²³)R²⁴,—C(O)N(R²⁵)R²⁶, SR²⁹, —C(O)SR³⁰ or —C(S)N(R²⁷)R²⁸ wherein R¹⁹ to R³⁰each independently represent hydrogen, unsubstituted or substituted arylor alkyl (which alkyl group itself may be unsubstituted or substitutedor terminated as defined herein) or, in the case of R²¹, halo, nitro,amino or cyano. The term “Het” thus includes groups such as optionallysubstituted azetidinyl, pyrrolidinyl, imidazolyl, indolyl, furanyl,oxazolyl, isoxazolyl, oxadiazolyl, thiazolyl, thiadiazolyl, triazolyl,oxatriazolyl, thiatriazolyl, pyridazinyl, morpholinyl, pyrimidinyl,pyrazinyl, quinolinyl, isoquinolinyl, piperidinyl, pyrazolyl andpiperazinyl. Substitution at Het may be at a carbon atom of the Het ringor, where appropriate, at one or more of the heteroatoms.

“Het” groups may also be in the form of an N oxide.

Suitable optional alcohols for use in the catalysed reaction of thepresent invention may be selected from

a C₁-C₃₀ alkanol, including aryl alcohols, which may be optionallysubstituted with one or more substituents selected from alkyl, aryl,Het, halo, cyano, nitro, OR¹⁹, OC(O)R²⁰, C(O)R²¹, C(O)OR²², NR²³R²⁴,C(O)NR²⁵R²⁶, C(S)NR²⁷R²⁸, SR²⁹ or C(O)SR³⁰ as defined herein. Highlypreferred alkanols are C₁-C₈ alkanols such as methanol, ethanol,propanol, iso-propanol, iso-butanol, t-butyl alcohol, phenol, n-butanoland chlorocapryl alcohol. Although the monoalkanols are most preferred,poly-alkanols, preferably, selected from di-octa ols such as diols,triols, tetra-ols and sugars may also be utilised. Typically, suchpolyalkanols are selected from 1,2-ethanediol, 1,3-propanediol,glycerol, 1,2,4 butanetriol, 2-(hydroxymethyl)-1,3-propanediol, 1,2,6trihydroxyhexane, pentaerythritol, 1,1,1 tri(hydroxymethyl)ethane,nannose, sorbase, galactose and other sugars. Preferred sugars includesucrose, fructose and glucose. Especially preferred alkanols aremethanol and ethanol. The most preferred alkanol is methanol. The amountof alcohol is not critical. Generally, amounts are used in excess of theamount of substrate to be esterified. Thus the alcohol may serve as thereaction solvent as well, although, if desired, separate or furthersolvents may also be used.

It will be appreciated that the end product of the reaction isdetermined at least in part by the source of alkanol used. For instance,use of methanol produces the corresponding methyl ester.

Typical conditions of temperature and pressure in the process of theinvention are between 100° C. and 400° C., more preferably, 200° C. and375° C., most preferably, 300° C. and 360° C.; between 0.001 MPa and 1MPa, more preferably, 0.03 MPa and 0.5 MPa, most preferably, between0.03 MPa and 0.3 MPa.

Contact times for the reactants in the presence of the catalyst aredependent on temperature, pressure, the nature of any support and theconcentration of the catalyst with respect to any support but aretypically between 0.05 and 300 secs, more preferably, 0.1 and 240 secs,most preferably, 0.5 and 120 secs, especially, 1 and 40 secs.

The amount of catalyst used in the process of the present invention isnot necessarily critical and will be determined by the practicalities ofthe process in which it is employed. However, the amount of catalystwill generally be chosen to effect the optimum selectivity and yield.Nevertheless, the skilled person will appreciate that the minimum amountof catalyst should be sufficient to bring about effective catalystsurface contact of the reactants during the contact time. In addition,the skilled person would appreciate that there would not really be anupper limit to the amount of catalyst relative to the reactants but thatin practice this may be governed again by the contact time required.

The relative amount of reagents in the process of the invention can varywithin wide limits but generally the mole ratio of formaldehyde orsuitable source thereof to the carboxylic acid or ester is within therange of 20:1 to 1:20, more preferably, 5:1 to 1:15, The most preferredratio will depend on the form of the formaldehyde and the ability of thecatalyst to liberate formaldehyde from the formaldehydic species. Thushighly reactive formaldehydic substances where one or both of R³¹ andR³² in R³¹O—(CH₂—O—)_(i)R³² is H require relatively low ratios,typically, in this case, the mole ratio of formaldehyde or suitablesource thereof to the carboxylic acid or ester is within the range of1:1 to 1:9. Where neither of R³¹ and R³² is H, as for instance inCH₃O—CH₂—OCH₃, or in trioxane higher ratios are most preferred,typically, 3:1 to 1:3.

As mentioned above, due to the source of formaldehyde, water may also bepresent in the reaction mixture. Depending on the source offormaldehyde, it may be necessary to remove some or all of the watertherefrom prior to catalysis. Maintaining lower levels of water thanthat in the source of formaldehyde may be advantageous to the catalyticefficiency and/or subsequent purification of the products. Water at lessthan 10 mole % in the reactor is preferred, more preferably, less than 5mole %, most preferably, less than 2 mole %.

The molar ratio of alcohol to the acid or ester is typically within therange 20:1 to 1:20, preferably 10:1 to 1:10, most preferably 5:1 to 1:5,for example 1:1. However the most preferred ratio will depend on theamount of water fed to the catalyst in the reactants plus the amountproduced by the reaction, so that the preferred molar ratio of thealcohol to the total water in the reaction will be at least 1:1 and morepreferably at least 3:1.

The reagents may be fed to the reactor independently or after priormixing and the process of reaction may be continuous or batch.Preferably, however, a continuous process is used.

Typically, the reaction takes place in the gas phase. Accordingly,suitable condensing equipment is generally required to condense theproduct stream after reaction has taken place. Similarly, a vaporisermay be used to bring the reactants up to temperature prior to thecatalyst bed.

DETAILED DESCRIPTION

It is to be understood by a person having ordinary skill in the art thatthe present discussion is a description of exemplary embodiments onlyand is not intended as limiting the broader aspects of the presentinvention. The following example is provided to further illustrate theinvention and is not to be construed to unduly limit the scope of theinvention. Embodiments of the invention will now be described withreference to the following non-limiting examples and by way ofillustration only.

EXPERIMENTAL

TABLE 1 MMA + MMA + MAA MAA MAA + Contact MAA selectivity selectivityMAA Catalyst time [s] yield [%] [%] [%] yield/s Comp AlPO 5.20 4.9 10.459.3 0.9 Ex. 1 Comp AlPO 1.47 4.8 12.9 78.0 3.3 Ex. 1 Ex. 1 AlPON 1.473.1 13.4 95.2 2.1 03750 Ex. 1 AlPON 5.20 03750 Ex. 2 AlPON 5.20 7.6 16.592.4 1.5 06750 Ex. 3 AlPON 5.20 8.1 17.3 93.5 1.6 15750

Comparative Example 1 AlPO

The acid catalyst that provided the base substrate for modification wasan amorphous aluminium phosphate (AlPO) prepared by a sol-gel methodinvolving co-gelation from a solution containing the component salts.

Co-Gelation Method

A high surface-area amorphous aluminium phosphate was prepared byco-gelation of a solution of salts containing the elements aluminium andphosphorus.

37.5 g of aluminium nitrate nonahydrate Al(NO₃)₃.9H₂O and 13.2 g ofdiammonium hydrogen phosphate (NH₄)₂HPO₄ were dissolved together in 160ml of demineralised water acidified with nitric acid HNO₃. Solution ofammonium hydroxide was added until pH 7 was reached. Formed hydrogel wasmixed for further 1 hr, after that it was filtered and washed withwater. It was dried at 80° C. overnight and then calcined in air at 600°C. for 1 hr. The calcined product was sieved to retain granules (0.5-1.4mm in diameter) for a catalyst testing.

Catalyst testing: 3 g of a catalyst was placed in a stainless steeltubular reactor connected to a vaporiser. The reactor was heated to 350°C. and vaporiser to 300° C. The mixture of 56.2 mole % of methylpropionate, 33.7 mole % of methanol, 9.6 mole % of formaldehyde and 0.5mole % of water was passed through. The condensed reaction mixture wasanalysed by gas chromatography equipped with CP-Sil 1701 column.

Example 1 AlPON 03750

Approximately 7 g of granule product from comparative example 1 wereplaced in an alumina boat in the centre of a tube furnace and heated at5° C./min ramp in a flow of dry nitrogen at the rate of 150 ml/min. At600° C. the gas feed was switched to dry ammonia at a rate of 150 ml/minwhile continuing to heat to 750° C. and maintained at this temperaturefor 3 hrs before the feed gas was switched back to dry nitrogen (150ml/min). The furnace was allowed to cool to below 100° C. before samplerecovery from the dry atmosphere.

Catalyst was tested as described in comparative example 1.

Example 2 AlPON 06750

Catalyst was prepared as in example 1, except that instead of 3 hrs ofammonia treatment 6 hrs were applied.

Catalyst was tested as described in comparative example 1.

Example 3 ALPON15750

Catalyst was prepared as in example 1, except that instead of 3 hrs ofammonia treatment 15 hrs was applied.

Catalyst was tested as described in comparative example 1.

TABLE 2 MMA + MMA + MAA MAA MMA + Contact MAA selectivity selectivityMAA Catalyst time [s] yield [%] [%] [%] yield/s Comp ZrPO 0.41 4.04 7.564.6 9.8 Ex. 2 Ex. 4 ZrPON 0.41 4.55 7.4 71.6 11.1 03750 Comp SnPO 2.002.1 11.0 64.3 1.0 Ex. 3 Ex. 5 SnPON 3.05 2.1 0.3 86.4 0.7 06400

Comparative Example 2 ZrPO

7.9 g of diammonium hydrogen phosphate (NH₄)₂HPO₄ dissolved in 50 ml ofdemineralised water were added dropwise to 19.3 g of zirconiumoxychloride ZrOCl₂.8H₂O dissolved in 200 ml of demineralised wateracidified with nitric acid HNO₃ and stirred for 2 hrs. It was filteredand washed with water, then dried at 110° C. overnight and calcined inair at 550° C. for 1 hr. Catalyst was tested as described in comparativeexample 1.

Example 4 ZrPON 03750

Approximately 7 g of granule product from comparative example 2 wereplaced in an alumina boat in the centre of a tube furnace and heated at5° C./min ramp in a flow of dry nitrogen at the rate of 150 ml/min. At600° C. the gas feed was switched to dry ammonia at a rate of 150 ml/minwhile continuing to heat to 750° C. and maintained at this temperaturefor 3 hrs before the feed gas was switched back to dry nitrogen (150ml/min). The furnace was allowed to cool to below 100° C. before samplerecovery from the dry atmosphere.

Catalyst was tested as described in comparative example 1.

Comparative Example 3 SnPO

13.0 g of tin chloride SnCl₄ in 200 ml of demineralised water was heatedto 50° C. and stirred with a magnetic bar while adding dropwise 7.1 g ofdiammonium hydrogen phosphate (NH₄)₂HPO₄ dissolved in 300 ml ofdemineralised water. The mixing was continued for 2 hrs. After that theproduct was filtered and washed with water. It was dried at 110° C.overnight and then calcined in air at 400° C. for 1 hr.

Catalyst was tested as described in comparative example 1.

Example 5 SnPON 06400

Approximately 7 g of granule product from comparative example 3 wereplaced in an alumina boat in the centre of a tube furnace and heated at5° C./min ramp in a flow of dry nitrogen at the rate of 150 ml/min. At250° C. the gas feed was switched to dry ammonia at a rate of 150 ml/minwhile continuing to heat to 400° C. and maintained at this temperaturefor 6 hrs before the feed gas was switched back to dry nitrogen (150ml/min). The furnace was allowed to cool to below 100° C. before samplerecovery from the dry atmosphere.

Catalyst was tested as described in comparative example 1.

TABLE 3 MMA + MMA + MAA MAA MMA + Contact MAA selectivity selectivityMAA Catalyst time [s] yield [%] [%] [%] yield/s Comp ZrNbO 0.6 5.5 3.880.6 9.2 Ex. 4 Comp GaSbO 1.12 6.5 1.9 77.8 5.8 Ex. 5

Comparative Example 4 ZrNbO

10.1 g of niobium chloride NbCl₅ in 25 ml of demineralised wateracidified with nitric acid HNO₃ were added to 12.1 g of zirconiumoxychloride ZrOCl₂.8H₂O in 25 ml of demineralised water acidified withnitric acid HNO₃ while stirring. After that a solution of ammoniumhydroxide was added until pH 7 was reached. This was aged for 1 hr, andthen it was filtered and washed with copious amount of water. It wasdried at 80° C. overnight and then calcined in air at 600° C. for 1 hr.

Catalyst was tested as described in comparative example 1.

Example 6 ZrNbON 06400

Approximately 7 g of granule product from comparative example 4 wereplaced in an alumina boat in the centre of a tube furnace and heated at5° C./min ramp in a flow of dry nitrogen at the rate of 150 ml/min. At250° C. the gas feed was switched to dry ammonia at a rate of 150 ml/minwhile continuing to heat to 400° C. and maintained at this temperaturefor 6 hrs before the feed gas was switched back to dry nitrogen (150ml/min). The furnace was allowed to cool to below 100° C. before samplerecovery from the dry atmosphere.

Catalyst was tested as described in comparative example 1 and found tohave improved selectivity.

Comparative Example 5 GaSbO

5 g of gallium chloride GaCl₃ in 25 ml of demineralised water acidifiedwith nitric acid HNO₃ were added dropwise to 8.6 g of antimony chlorideSbCl₅ in 5 ml of demineralised water while stirring. Subsequently asolution of ammonium hydroxide was added until pH 7 was reached. Thereaction mixture was aged for 1 hr, after that it was filtered andwashed with copious amount of water. It was dried at 80° C. overnightand then calcined in air at 600° C. for 1 hr. Catalyst was tested asdescribed in comparative example 1.

Example 7 GaSbON 06400

Approximately 7 g of granule product from comparative example 5 wereplaced in an alumina boat in the centre of a tube furnace and heated at5° C./min ramp in a flow of dry nitrogen at the rate of 150 ml/min. At250° C. the gas feed was switched to dry ammonia at a rate of 150 ml/minwhile continuing to heat to 400° C. and maintained at this temperaturefor 6 hrs before the feed gas was switched back to dry nitrogen (150ml/min). The furnace was allowed to cool to below 100° C. before samplerecovery from the dry atmosphere.

Catalyst was tested as described in comparative example 1 and found tohave improved selectivity.

TABLE 4 MMA + MAA MAA MAA + Contact MMA + MAA selectivity selectivityMAA Catalyst time [s] yield [%] [%] [%] yield/s Comp. Ex. 6Ga_(0.1)Al_(0.9)PO 2.40 4.3 10.4 64.1 1.8 Ex. 8 Ga_(0.1)Al_(0.9)PON 2.366.4 11.7 75.2 2.7 03750 Ex. 9 Ga_(0.1)Al_(0.9)PON 2.32 5.5 4.9 80.9 2.415750

Comparative Example 6 Ga0.1Al0.9PO

5 g of gallium chloride, 34 g of aluminium chloride AlCl₃ were mixedwith 19.4 g of phosphoric acid H₃PO₄ in 122 ml of demineralised water.This was cooled to 0° C. in a dry ice alcohol bath. Subsequently a largeexcess of propylene oxide was slowly added under vigorous stirring. Thesolution turned into a translucent gel after a few hours. The productwas washed with isopropanol. It was dried at 110° C. overnight and thencalcined in air at 650° C. for 1 hr. Catalyst was tested as described incomparative example 1.

Example 8 Ga0.1Al0.9PON 03750

Approximately 7 g of granule product from comparative example 6 wereplaced in an alumina boat in the centre of a tube furnace and heated at5° C./min ramp in a flow of dry nitrogen at the rate of 150 ml/min. At600° C. the gas feed was switched to dry ammonia at a rate of 150 ml/minwhile continuing to heat to 750° C. and maintained at this temperaturefor 3 hrs before the feed gas was switched back to dry nitrogen (150ml/min). The furnace was allowed to cool to below 100° C. before samplerecovery from the dry atmosphere.

Catalyst was tested as described in comparative example 1.

Example 9 Ga0.1Al0.9PON 15750

Catalyst was prepared as in example 8, except that instead of 3 hrs ofammonia treatment 15 hrs was applied.

Catalyst was tested as described in comparative example 1.

TABLE 5 MMA + MMA + MAA MAA MMA + Contact MAA selectivity selectivityMAA Catalyst time [s] yield [%] [%] [%] yield/s Comp. ZrO₂ 0.89 5.8 1.550.9 6.5 Ex. 7 Comp. ZrON 4.58 5.7 0.5 50.0 1.2 Ex. 8 15500 Comp. SiO₂10.03 0.15 — — 0.015 Ex. 9 Comp. SiON 14.57 0.6 — — 0.04 Ex. 10 (Grace)15400 Comp. SiON 8.53 0.6 — — 0.07 Ex. 11 (Grace) 15750 Comp. Al₂O₃ 4.05.6 6.3 64.0 10.2 Ex. 12 Comp. AlON 5.6 5.6 7.6 60.0 10.4 Ex. 13 03750

Comparative Example 7 ZrO₂

14.5 g of zirconium oxychloride octahydrate ZrOCl₂.8H₂O were dissolvedin 300 ml of demineralised water and stirred continuously while adding10 ml of 30% ammonia in 110 ml of water. The suspension was agitated atroom temperature for 3 hrs, then filtered and washed with water toremove any residues of chloride. The product was dried at 80° C.overnight and calcined at 500° C. for 1 hr.

Catalyst was tested as described in comparative example 1.

Comparative Example 8 ZrON 15500

Approximately 7 g of granule product from comparative example 7 wereplaced in an alumina boat in the centre of a tube furnace and heated at5° C./min ramp in a flow of dry nitrogen at the rate of 150 ml/min. At350° C. the gas feed was switched to dry ammonia at a rate of 150 ml/minwhile continuing to heat to 500° C. and maintained at this temperaturefor 15 hrs before the feed gas was switched back to dry nitrogen (150ml/min). The furnace was allowed to cool to below 100° C. before samplerecovery from the dry atmosphere.

Catalyst was tested as described in comparative example 1.

Comparative Example 9 SiO₂

Pure SiO₂ beads were purchased from Grace.

Catalyst was tested as described in comparative example 1.

Comparative example 10 SiON (Grace) 15400 Approximately 7 g of granuleproduct from comparative example 9 were placed in an alumina boat in thecentre of a tube furnace and heated at 5° C./min ramp in a flow of drynitrogen at the rate of 150 ml/min. At 250° C. the gas feed was switchedto dry ammonia at a rate of 150 ml/min while continuing to heat to 400°C. and maintained at this temperature for 15 hrs before the feed gas wasswitched back to dry nitrogen (150 ml/min). The furnace was allowed tocool to below 100° C. before sample recovery from the dry atmosphere.

Catalyst was tested as described in comparative example 1.

Comparative Example 11 SiON (Grace) 15750

Approximately 7 g of granule product from comparative example 9 wereplaced in an alumina boat in the centre of a tube furnace and heated at5° C./min ramp in a flow of dry nitrogen at the rate of 150 ml/min. At600° C. the gas feed was switched to dry ammonia at a rate of 150 ml/minwhile continuing to heat to 750° C. and maintained at this temperaturefor 15 hrs before the feed gas was switched back to dry nitrogen (150ml/min). The furnace was allowed to cool to below 100° C. before samplerecovery from the dry atmosphere.

Catalyst was tested as described in comparative example 1.

Comparative Example 12 Al₂O₃

75.0 g of aluminium nitrate were dissolved in demineralised water, whichwas acidified with drops of nitric acid to aid dissolution. The gel wasprecipitated by addition of aqueous ammonia. The gel was filtered andwashed with water. After drying overnight at 110° C., it was calcined at500° C. in air flow for 1 hr.

Catalyst was tested as described in comparative example 1.

Comparative Example 13 AlON 03750

Approximately 7 g of granule product from comparative example 12 wereplaced in an alumina boat in the centre of a tube furnace and heated at5° C./min ramp in a flow of dry nitrogen at the rate of 150 ml/min. At600° C. the gas feed was switched to dry ammonia at a rate of 150 ml/minwhile continuing to heat to 750° C. and maintained at this temperaturefor 3 hrs before the feed gas was switched back to dry nitrogen (150ml/min). The furnace was allowed to cool to below 100° C. before samplerecovery from the dry atmosphere.

Catalyst was tested as described in comparative example 1.

Several examples were tested for the generation of side products in thecondensed reaction mixture. Three side products that may proveproblematic during separation in an industrial process due to theirbeing close in boiling point to one of the desired end products, methylmethacrylate, were tested. These are toluene, diethyl ketone and methylisobutyrate. The results are shown in table 6 and show a markedreduction in such impurities for the nitrided mixed oxides compared withboth non-nitrided mixed oxides and nitrided single metal oxides.

TABLE 6 Contact MIB DEK toluene Catalyst time [s] [mole %] [mole %][mole %] Comp. Ex. 1 AlPO 1.83 0.0240 0.0547 0.0054 Ex. 1 AlPON 1.470.0013 0.0031 0.0003 03750 Ex. 2 AlPON 5.20 0.0126 0.0038 0.0008 06750Comp. Ex. 2 ZrPO 0.42 0.0228 0.0569 0.0042 Ex. 4 ZrPON 0.41 0.01500.0370 0.0028 03750 Comp. Ex. 7 ZrO2 1.01 0.1819 0.7004 0.0001 Comp. Ex.8 ZrON 4.70 0.2591 0.8241 0.0001 15500

Attention is directed to all papers and documents which are filedconcurrently with or previous to this specification in connection withthis application and which are open to public inspection with thisspecification, and the contents of all such papers and documents areincorporated herein by reference.

All of the features disclosed in this specification (including anyaccompanying claims, abstract and drawings), and/or all of the steps ofany method or process so disclosed, may be combined in any combination,except combinations where at least some of such features and/or stepsare mutually exclusive.

Each feature disclosed in this specification (including any accompanyingclaims, abstract and drawings) may be replaced by alternative featuresserving the same, equivalent or similar purpose, unless expressly statedotherwise. Thus, unless expressly stated otherwise, each featuredisclosed is one example only of a generic series of equivalent orsimilar features.

The invention is not restricted to the details of the foregoingembodiment(s). The invention extends to any novel one, or any novelcombination, of the features disclosed in this specification (includingany accompanying claims, abstract and drawings), or to any novel one, orany novel combination, of the steps of any method or process sodisclosed.

What is claimed is:
 1. A method of producing an ethylenicallyunsaturated carboxylic acid or ester comprising the steps of contactingformaldehyde or a suitable source thereof with a carboxylic acid orester in the presence of a catalyst and optionally in the presence of analcohol, wherein the catalyst comprises a nitrided metal oxide having atleast two types of metal cations, M¹ and M², wherein M¹ is selected fromthe metals of group 3, 4, 13 (called also IIIA) or 14 (called also IVA)of the periodic table and M² is selected from the metals of groups 5 or15 (called also VA) of the periodic table.
 2. A method according toclaim 1, wherein the nitrided metal oxide consists of two to four metalcations, and oxygen and nitrogen anions.
 3. A method according to claim1, wherein the M¹ type of metal is selected from one or more metals inthe list consisting of:—B, Al, Ga, In, Tl, Sc, Y, La, Ac, Si, Ge, Sn,Pb, Ti, Zr, Hf and Rf.
 4. A method according to claim 1, wherein the M²type of metal is selected from one or more metals in the list consistingof:—P(5+), Nb(5+), As(5+) Sb(5+) and Ta(5+).
 5. A method according toclaim 1, wherein the nitrided metal oxide is selected from the listconsisting of:—AlPON; ZrPON; SnPON; ZrNbON; GaSbON; and GaAlPON, eitherunsupported or supported on a suitable support, for example, alumina,silica, silicon nitride, colloidal silica, titania or aluminiumphosphate.
 6. The method of claim 1, wherein the nitrided metal oxide issupported on a support selected from the group consisting of: alumina,silica, silicon nitride, colloidal silica, titania or aluminiumphosphate.
 7. A method according to claim 1, wherein a further metal ormetal cation of the type M³ is also present in the nitrided mixed metaloxide wherein M³ metals include metals from group I of the periodictable.
 8. A method according to claim 1, wherein the nitrided metaloxide formula is: M¹ _(n)M² _(m)M³ _(q)O_(p)N_(s) wherein M¹ is acation, preferably, a 3+ cation and M² is a cation, preferably, a 5+cation, n, m, p and s may be a positive integer or decimal number and qmay be a positive integer or decimal number or zero.
 9. The method ofclaim 8, wherein M¹ is a 3+ cation and M² is a 5+ cation.
 10. A methodaccording to claim 1, wherein the carboxylic acid or ester reactant isof formula R³—CH₂—COOR⁴ wherein R⁴ is either hydrogen or an alkyl groupand R³ is either hydrogen, an alkyl or aryl group.
 11. A methodaccording to claim 1, wherein the ethylenically unsaturated acid orester produced by the process of the invention is selected frommethacrylic acid, acrylic acid, methyl methacrylate, ethyl acrylate orbutyl acrylate.
 12. The method of claim 1, wherein the step ofcontacting formaldehyde with a carboxylic acid or ester in the presenceof a catalyst is also carried out in the presence on alcohol.
 13. Themethod of claim 1, wherein the ethylenically unsaturated carboxylic acidor ester is produced with a catalyst system by contacting formaldehydeor a suitable source thereof with a carboxylic acid or ester in thepresence of a catalyst of the catalyst system, wherein the catalystcomprises a nitrided metal oxide having at least two types of metalcations, M¹ and M², wherein M¹ is selected from the metals of group 3,4, 13 (called also IIIA) or 14 (called also IVA) of the periodic tableand M² is selected from the metals of groups 5 or 15 (called also VA) ofthe periodic table to produce the ethylenically unsaturated carboxylicacid or ester.
 14. The method of claim 1, wherein the ethylenicallyunsaturated carboxylic acid or ester is an α,β ethylenically unsaturatedacid.
 15. A catalyst system for the reaction of formaldehyde or asuitable source thereof with a carboxylic acid or ester to produce anethylenically unsaturated carboxylic acid or ester wherein the catalystcomprises a nitrided metal oxide having at least two types of metalcations, M¹ and M², wherein M¹ is selected from at least two metals ofgroup 3, 4, 13 (called also IIIA), 14 (called also IVA) of the periodictable and M² is selected from at least one metal of group 5 or at leastone metal of group 15 (called also VA) in the 4^(th) to 6^(th) periodsof the periodic table.
 16. A catalyst system according to claim 15,wherein the nitrided metal oxide consists of two to four metal cations,and oxygen and nitrogen anions.
 17. A catalyst system according to claim15, wherein the nitrided metal oxide formula is: M² _(x)M²_(y)O_(n)N_(z) wherein z is the average number of nitrogen atoms andwherein x, y, n and z may each be a positive decimal number or integer.18. A catalyst system according to claim 15, wherein the M¹ type ofmetal is selected from two or more metals in the list consisting of:—B,Al, Ga, In, Tl, Sc, Y, La, Ac, Si, Ge, Sn, Pb, Ti, Zr, Hf and Rf.
 19. Acatalyst system according to claim 15, wherein the M² type of metal isselected from one or more metals in the list consisting of:—Nb(5+), As(5+) Sb(5+) and Ta(5+).
 20. The catalyst of claim 15, wherein thenitrided metal oxide is supported on a support selected from the groupconsisting of: alumina, silica, silicon nitride, colloidal silica,titania or aluminium phosphate.
 21. A catalyst system according to claim15, wherein a further metal or metal cation of the type M³ is alsopresent in the nitrided mixed metal oxide and wherein M³ metals includemetals from group I of the periodic table.
 22. The catalyst system ofclaim 15, wherein the reaction of formaldehyde or a suitable sourcethereof with a carboxylic acid or ester is also carried out in thepresence on alcohol.
 23. The catalyst of claim 15, wherein theethylenically unsaturated carboxylic acid or ester is an α,βethylenically unsaturated acid.
 24. A catalyst system for the reactionof formaldehyde or a suitable source thereof with a carboxylic acid orester to produce an ethylenically unsaturated carboxylic acid or esterwherein the catalyst comprises a nitrided metal oxide having at leasttwo types of metal cations, M¹ and M², wherein M¹ is selected from themetals of group 3, 4, 13 (called also IIIA) or 14 (called also IVA) ofthe periodic table and M² is selected from the metals of groups 5 or 15(called also VA) of the periodic table, wherein the nitrided metal oxideis supported on a support selected from the group consisting of:alumina, silica, silicon nitride, colloidal silica, titania or aluminiumphosphate.